Bioflavoring by non-conventional yeasts in sequential beer fermentations

Modifying flavor profiles of Saccharomyces spp. for industrial brewing using FIND-IT, a non-GMO approach for metabolic engineering of yeast

Species of Saccharomyces genus have played an irreplaceable role in alcoholic beverage and baking industry for centuries. S. cerevisiae has also become an organism of choice for industrial production of alcohol and other valuable chemicals and a model organism shaping the rise of modern genetics and genomics in the past few decades. Today´s brewing industry faces challenges of decreasing consumption of traditional beer styles and increasing consumer demand for new styles, flavors and aromas. The number of currently used brewer's strains and their genetic diversity is yet limited and implementation of more genetic and phenotypic variation is seen as a solution to cope with the market challenges. This requires modification of current production strains or introduction of novel strains from other settings, e.g. industrial or wild habitats into the brewing industry. Due to legal regulation in many countries and negative customer perception of GMO organisms, the production of food and beverages requires non-GMO production organisms, whose development can be difficult and time-consuming. Here, we apply FIND-IT (Fast Identification of Nucleotide variants by DigITal PCR), an ultrafast genome-mining method, for isolation of novel yeast variants with varying flavor profiles. The FIND-IT method uses combination of random mutagenesis, droplet digital PCR with probes that target a specific desired mutation and a sub-isolation of the mutant clone. Such an approach allows the targeted identification and isolation of specific mutant strains with eliminated production of certain flavor and off-flavors and/or changes in the strain metabolism. We demonstrate that the technology is useful for the identification of loss-of function or gain of function mutations in unrelated industrial and wild strains differing in ploidy. Where no other phenotypic selection exists, this technology serves together with standard breeding techniques as a modern tool facilitating a modification of (brewer's) yeast strains leading to diversification of the product portfolio.

Visualizing Metabolism in Biotechnologically Important Yeasts with dDNP NMR Reveals Evolutionary Strategies and Glycolytic Logic

Saccharomyces cerevisiae has long been a pillar of biotechnological production and basic research. More recently, strides to exploit the functional repertoire of nonconventional yeasts for biotechnological production have been made. Genomes and genetic tools for these yeasts are not always available, and yeast genomics alone may be insufficient to determine the functional features in yeast metabolism. Hence, functional assays of metabolism, ideally in the living cell, are best suited to characterize the cellular biochemistry of such yeasts. Advanced in cell NMR methods can allow the direct observation of carbohydrate influx into central metabolism on a seconds time scale: dDNP NMR spectroscopy temporarily enhances the nuclear spin polarization of substrates by more than 4 orders of magnitude prior to functional assays probing central metabolism. We use various dDNP enhanced carbohydrates for in-cell NMR to compare the metabolism of S. cerevisiae and nonconventional yeasts, with an emphasis on the wine yeast Hanseniaspora uvarum. In-cell observations indicated more rapid exhaustion of free cytosolic NAD+ in H. uvarum and alternative routes for pyruvate conversion, in particular, rapid amination to alanine. In-cell observations indicated that S. cerevisiae outcompetes other biotechnologically relevant yeasts by rapid ethanol formation due to the efficient adaptation of cofactor pools and the removal of competing reactions from the cytosol. By contrast, other yeasts were better poised to use redox neutral processes that avoided CO2-emission. Beyond visualizing the different cellular strategies for arriving at redox neutral end points, in-cell dDNP NMR probing showed that glycolytic logic is more conserved: nontoxic precursors of cellular building blocks formed high-population intermediates in the influx of glucose into the central metabolism of eight different biotechnologically important yeasts. Unsupervised clustering validated that the observation of rapid intracellular chemistry is a viable means to functionally classify biotechnologically important organisms.

Influence of climatic variation on microbial communities during organic Pinot noir wine production

To assess the possible impact of climatic variation on microbial community composition in organic winemaking, we employed a metabarcoding approach to scrutinize the microbiome in a commercial, organic, Pinot noir wine production system that utilizes autochthonous fermentation. We assessed microbial composition across two vintages (2018 and 2021) using biological replicates co-located at the same winery. Microbial dynamics were monitored over four important fermentation time points and correlated with contemporaneous climate data. Bacterial (RANOSIM = 0.4743, p = 0.0001) and fungal (RANOSIM = 0.4738, p = 0.0001) compositions were different in both vintages. For bacteria, Lactococcus dominated the diversity associated with the 2018 vintage, while Tatumella dominated the 2021 vintage. For fungal populations, while Saccharomyces were abundant in both vintages, key differences included Starmerella, copious in the 2018 vintage; and Metschnikowia, substantive in the 2021 vintage. Ordination plots correlated the climatic variables with microbial population differences, indicating temperature as a particularly important influence; humidity values also differed significantly between these vintages. Our data illustrates how climatic conditions may influence microbial diversity during winemaking, and further highlights the effect climate change could have on wine production.

Recycled Brewer's Spent Grain (BSG) and Grape Juice: A New Tool for Non-Alcoholic (NAB) or Low-Alcoholic (LAB) Craft Beer Using Non-Conventional Yeasts

Non-alcoholic beer (NAB) and low-alcoholic beer (LAB) are taking over the market with growing sales. Sustainable recycling and valorization of exhausted brewer's spent grain (BSG) coming from craft beer is a relevant issue in the brewing process. In this work, recycled BSG and BSG + GJ (supplemented with 10% grape juice) were used as a wort substrate to inoculate Lachancea thermotolerans, Wickeramhomyces anomalus, Torulaspora delbruecki and Pichia kluyveri non-conventional yeasts to produce NABLAB craft beer. Results showed that wort composed of only recycled BSG produced appreciated NAB beers (ethanol concentration from 0.12% to 0.54% v/v), while the addition of 10% grape juice produced LAB beers (ethanol concentration from 0.82 to 1.66% v/v). As expected, volatile compound production was highest with the addition of grape juice. L. thermotolerans showed lactic acid production, characterizing both worts with the production of ethyl butyrate and isoamyl acetate. T. delbrueckii exhibited relevant amounts of hexanol, phenyl ethyl acetate and β-phenyl ethanol (BSG + GJ). W. anomalus and P. kluyveri showed consistent volatile production, but only in BSG + GJ where fermentation activity was exhibited. The overall results indicated that reused BSGs, non-conventional yeasts and grape juice are suitable bioprocesses for specialty NABLAB beer.

The potential for Scotch Malt Whisky flavour diversification by yeast

Scotch Whisky, a product of high importance to Scotland, has gained global approval for its distinctive qualities derived from the traditional production process, which is defined in law. However, ongoing research continuously enhances Scotch Whisky production and is fostering a diversification of flavour profiles. To be classified as Scotch Whisky, the final spirit needs to retain the aroma and taste of 'Scotch'. While each production step contributes significantly to whisky flavour-from malt preparation and mashing to fermentation, distillation, and maturation-the impact of yeast during fermentation is crucially important. Not only does the yeast convert the sugar to alcohol, it also produces important volatile compounds, e.g. esters and higher alcohols, that contribute to the final flavour profile of whisky. The yeast chosen for whisky fermentations can significantly influence whisky flavour, so the yeast strain employed is of high importance. This review explores the role of yeast in Scotch Whisky production and its influence on flavour diversification. Furthermore, an extensive examination of nonconventional yeasts employed in brewing and winemaking is undertaken to assess their potential suitability for adoption as Scotch Whisky yeast strains, followed by a review of methods for evaluating new yeast strains.

Screening ester-producing yeasts to fortify the brewing of rice-flavor Baijiu for enhanced aromas

To enhance the aromas in Guangdong rice-flavor Baijiu, ester-producing yeast was selected to fortify Baijiu brewing. Among eight kinds of ester-producing yeasts selected, Saccharomyces cerevisiae CM15 (CM15) that showed both the stronger ability to utilize substrates to produce esters and the excellent tolerance to industrially relevant stress factors was chosen. When CM15 was synergistically fermented with six kinds of Kojis from distilleries of rice-flavor liquor in Guangdong, the enhanced total esters had happened to the liquors brewing with the fortified four kinds of Kojis, especially with Koji F. When Koji F was fortified with CM15, the resultant Baijiu showed a higher esters proportion and a lower higher alcohol ratio than that of Baijiu brewed only with Koji F, with the content of ethyl acetate and ethyl lactate increasing by 25% and 214%, respectively. This study suggested that CM15 can be used as a functional microorganism to fortify Baijiu brewing, which might also be suitable for other traditional fermented foods.

Technological and Organoleptic Parameters of Craft Beer Fortified with Powder of the Culinary-Medicinal Mushroom Pleurotus eryngii

Beer is one of the oldest and most popular alcoholic beverages and is currently consumed worldwide. The various components used in the brewing process have a physiological impact on the consumer and current research aims to improve its technological and functional properties through the addition of natural compounds (plants or mushrooms). In this work, the addition of two different amounts (5 and 10 g/L) of Pleurotus eryngii var. eryngii in powder form added at different production stages (PRE and POST alcoholic fermentation) showed the improvement in yeast viability during the alcoholic fermentation, increased the alcoholic content, and improved the sensorial profile. Regarding the organoleptic profile in the experimental samples, cocoa/chocolate and mushroom aromas were found and the samples PRE10 and POST5 received the best ratings with respect to all evaluated parameters.

The marula and elephant intoxication myth: assessing the biodiversity of fermenting yeasts associated with marula fruits (Sclerocarya birrea)

The inebriation of wild African elephants from eating the ripened and rotting fruit of the marula tree is a persistent myth in Southern Africa. However, the yeasts responsible for alcoholic fermentation to intoxicate the elephants remain poorly documented. In this study, we considered Botswana, a country with the world's largest population of wild elephants, and where the marula tree is indigenous, abundant and protected, to assess the occurrence and biodiversity of yeasts with a potential to ferment and subsequently inebriate the wild elephants. We collected marula fruits from over a stretch of 800 km in Botswana and isolated 106 yeast strains representing 24 yeast species. Over 93% of these isolates, typically known to ferment simple sugars and produce ethanol comprising of high ethanol producers belonging to Saccharomyces, Brettanomyces, and Pichia, and intermediate ethanol producers Wickerhamomyces, Zygotorulaspora, Candida, Hanseniaspora, and Kluyveromyces. Fermentation of marula juice revealed convincing fermentative and aromatic bouquet credentials to suggest the potential to influence foraging behaviour and inebriate elephants in nature. There is insufficient evidence to refute the aforementioned myth. This work serves as the first work towards understanding the biodiversity marula associated yeasts to debunk the myth or approve the facts.

Sour Beer as Bioreservoir of Novel Craft Ale Yeast Cultures

The increasing demand for craft beer is driving the search for novel ale yeast cultures from brewing-related wild environments. The focus of bioprospecting for craft cultures is to identify feral yeasts suitable to imprint unique sensorial attributes onto the final product. Here, we integrated phylogenetic, genotypic, genetic, and metabolomic techniques to demonstrate that sour beer during aging in wooden barrels is a source of suitable craft ale yeast candidates. In contrast to the traditional lambic beer maturation phase, during the aging of sour-matured production-style beer, different biotypes of Saccharomyces cerevisiae dominated the cultivable in-house mycobiota, which were followed by Pichia membranifaciens, Brettanomyces bruxellensis, and Brettanomyces anomalus. In addition, three putative S. cerevisiae × Saccharomyces uvarum hybrids were identified. S. cerevisiae feral strains sporulated, produced viable monosporic progenies, and had the STA1 gene downstream as a full-length promoter. During hopped wort fermentation, four S. cerevisiae strains and the S. cerevisiae × S. uvarum hybrid WY213 exceeded non-Saccharomyces strains in fermentative rate and ethanol production except for P. membranifaciens WY122. This strain consumed maltose after a long lag phase, in contrast to the phenotypic profile described for the species. According to the STA1+ genotype, S. cerevisiae partially consumed dextrin. Among the volatile organic compounds (VOCs) produced by S. cerevisiae and the S. cerevisiae × S. uvarum hybrid, phenylethyl alcohol, which has a fruit-like aroma, was the most prevalent. In conclusion, the strains characterized here have relevant brewing properties and are exploitable as indigenous craft beer starters.

A multivariate approach to explore the volatolomic and sensory profiles of craft Italian Grape Ale beers produced with novel Saccharomyces cerevisiae strains

This study investigated the influence of three Saccharomyces cerevisiae strains, selected from different matrices - CHE-3 (cherry), P4 (sourdough) and TA4-10 (grape must) - on characteristics of Italian Grape Ale (IGA) beers obtained at microbrewery scale. A multidisciplinary approach, combining results from analysis of chemical, volatile and organoleptic profiles of the beers, was adopted to underline the relationships between yeast starter and the quality of final products. Detection volatile organic compounds (VOCs) by Gas-Chromatography coupled with Mass Spectrometry (GC-MS) after extraction carried out by head-space micro-extraction (HS-SPME) revealed that the beer obtained by P4 strain differed from the others for its higher concentrations of esters, alcohols, and terpenes as confirmed by PCA (principal component analysis) and Cluster heatmap. Furthermore, sensorial analysis and consumer test showed that this sample differed from others by more pronounced notes of "fruity smell and floral" and "olfactory finesse," and it was the most appreciated beer for smell, taste, and overall quality. Conversely, CHE-3 was the sample with the lowest concentrations of the identified volatiles and, together TA4-10, showed the highest scores for smoked, yeast, malt, and hop notes. As far as we know, these are the first results on the application of indigenous S. cerevisiae strains in the production of craft IGA beers analyzed through a complex multivariate approach.

The optimization of sequential fermentation in the dealcoholized apple juice for reducing lipids

Yeast and lactic acid bacteria are widely used in fermented foods and the nutrients and metabolites produced by fermentation have cholesterol degrading effects. This study utilized Xinjiang Aksu apples as the material to optimize the sequential fermentation process of different strains and construct a fermentation kinetic model to develop a functional fermentation product with low-sugar, probiotics-rich and lipid-lowering properties. The sequential fermentation of dealcoholized apple juice with Saccharomyces cerevisiae and Lactobacillus plantarum was optimized by response surface design, based on which a sequential fermentation kinetic model was constructed. The changes of short-chain fatty acids, cholesterol elimination rate and hydrophobic properties during the fermentation process were studied. The results showed that the kinetic model established under the optimal conditions could effectively predict the dynamic changes of the basic indexes during the fermentation process. After fermentation, the viable number of L. plantarum was 4.96 × 108 CFU/mL, short-chain fatty acids increased, the cholesterol elimination rate reached 45.06%, and the hydrophobicity was 51.37%, which had favorable lipid-lowering properties and hydrophobic effect. This research will provide a theoretical basis and technical support for the monitoring of microbial dynamics and functionalization development of sequentially fermented apple juice with different strains.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05741-z.

Study of a First Approach to the Controlled Fermentation for Lambic Beer Production

Non-Saccharomyces yeasts represent a great source of biodiversity for the production of new beer styles, since they can be used in different industrial areas, as pure culture starters, in co-fermentation with Saccharomyces, and in spontaneous fermentation (lambic and gueuze production, with the main contribution of Brettanomyces yeast). The fermentation process of lambic beer is characterized by different phases with a characteristic predominance of different microorganisms in each of them. As it is a spontaneous process, fermentation usually lasts from 10 months to 3 years. In this work, an attempt was made to perform a fermentation similar to the one that occurred in this process with lactic bacteria, Saccharomyces yeast and Brettanomyces yeast, but controlling their inoculation and therefore decreasing the time necessary for their action. For this purpose, after the first screening in 100 mL where eight Brettanomyces yeast strains from D.O. "Ribeira Sacra" (Galicia) were tested, one Brettanomyces bruxellensis strain was finally selected (B6) for fermentation in 1 L together with commercial strains of Saccharomyces cerevisiae S-04 yeast and Lactobacillus brevis lactic acid bacteria in different sequences. The combinations that showed the best fermentative capacity were tested in 14 L. Volatile compounds, lactic acid, acetic acid, colour, bitterness, residual sugars, ethanol, melatonin and antioxidant capacity were analysed at different maturation times of 1, 2, 6 and 12 months. Beers inoculated with Brettanomyces yeast independently of the other microorganisms showed pronounced aromas characteristic of the Brettanomyces yeast. Maturation after 12 months showed balanced beers with "Brett" aromas, as well as an increase in the antioxidant capacity of the beers.

A special drop: Characterising yeast isolates associated with fermented beverages produced by Australia's indigenous peoples

Way-a-linah, an alcoholic beverage produced from the fermented sap of Eucalyptus gunnii, and tuba, a fermented drink made from the syrup of Cocos nucifera fructifying bud, are two of several fermented beverages produced by Australian Aboriginal and Torres Strait people. Here we describe the characterisation of yeast isolates from samples associated with the fermentation of way-a-linah and tuba. Microbial isolates were obtained from two different geographical locations in Australia - the Central Plateau in Tasmania, and Erub Island in the Torres Strait. While Hanseniaspora species and Lachancea cidri were the most abundant species in Tasmania, Candida species were the most abundant in Erub Island. Isolates were screened for tolerance to stress conditions found during the production of fermented beverages and for enzyme activities relevant to the appearance, aroma and flavour of these beverages. Based on screening results, eight isolates were evaluated for their volatile profile during the fermentation of wort, apple juice and grape juice. Diverse volatile profiles were observed for beers, ciders and wines fermented with different isolates. These findings reveal the potential of these isolates to produce fermented beverages with unique aroma and flavour profiles and highlight the vast microbial diversity associated with fermented beverages produced by Australia's Indigenous peoples.

Identification and assessment of non-conventional yeasts in mixed fermentations for brewing bioflavored beer

The increasing demand for more flavored and complex beers encourages the investigation of novel and non-conventional yeasts with the ability to provide a combination of bioflavoring and low ethanol yields. The present study identified 22 yeasts isolated from different brewing sources, including the fermentation by-products known as yeast sludges, and characterized a selection of strains to find the more suitable for the aforementioned aims. HPLC and GC-FID analysis of its brewing products were performed. The most promising results were obtained with the non-conventional yeasts Pichia kudriavzevii MBELGA61 and Meyerozyma guilliermondii MUS122. The former, isolated from a Belgian wheat beer sludge, was capable of growing in wort (17.0°Bx., 20 °C) with very low ethanol yields (1.19 % v/v). Besides, upon mixed fermentations with Saccharomyces cerevisiae, was suitable to produce volatile compounds such as ethyl acetate, 2-phenyl ethanol and isoamyl alcohol, with characteristic fruity notes. M. guilliermondii MUS122, isolated from a golden ale beer sludge, partially attenuated the wort with low production of ethanol and biomass. In addition, provided some fruity and floral nuances to the aroma profile of mixed fermentations with brewer's yeast. The results suggest that these strains favor the development of more fruity-flowery aroma profiles in beers. Furthermore, they are suitable for use in mixed fermentations with Saccharomyces brewer's strains, although the ethanol level did not decrease significantly.

The Influence of Pichia kluyveri Addition on the Aroma Profile of a Kombucha Tea Fermentation

Traditional kombucha is a functional tea-based drink that has gained attention as a low or non-alcoholic beverage. The fermentation is conducted by a community of different microorganisms, collectively called SCOBY (Symbiotic Culture of Bacteria and Yeast) and typically consists of different acetic acid bacteria and fermenting yeast, and in some cases lactic acid bacteria that would convert the sugars into organic acids-mostly acetic acid. In this study, the effect of including a Pichia kluyveri starter culture in a kombucha fermentation was investigated. P. kluyveri additions led to a quicker accumulation of acetic acid along with the production of several acetate esters including isoamyl acetate and 2-phenethyl acetate. A subsequent tasting also noted a significant increase in the fruitiness of the kombucha. The significant contribution to the aroma content shows the promise of this yeast in future microbial formulations for kombucha fermentations.

Production and sensory analysis of grape flavoured beer by co-fermentation of an industrial and a genetically modified laboratory yeast strain

The so-called "craft beer revolution" has increased the demand for new styles of beers, often with new ingredients like flavour extracts. In recent years, synthetic biology has realized the production of a plethora of plant secondary metabolites in microbial hosts, which could provide an alternative source for these compounds. In this study, we selected a in situ flavour production approach for grape flavour addition. We used an O-methyl anthranilate (OmANT) producing laboratory Saccharomyces cerevisiae strain in co-fermentations with an industrial beer yeast strain WLP644. The laboratory strain provided an ease of genetic manipulation and the desirable properties of the WLP644 strain were not modified in this approach. In shake flasks, a 10:90 ratio of the yeasts produced grape flavoured beer with the yeast produced flavour compound in a range normally used for flavoured beverages. Hopped and unhopped beers were analysed by VTT's trained sensory panel and with olfactory GC-MS. OmANT was successfully detected from the beers as a floral odour and flavour. Moreover, no off-flavours were detected and aroma profiles outside the grape flavour were rather similar. These results indicate that the co-fermentation principle is a suitable approach to change the flavour profiles of beers with a simple yeast strain drop-in approach.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00217-023-04274-1.

Brewing a Craft Belgian-Style Pale Ale Using Pichia kudriavzevii 4A as a Starter Culture

There is an expanding market for beer of different flavors. This study aimed to prepare a craft Belgian-style pale ale with a non-Saccharomyces yeast. Pichia kudriavzevii 4A was used as a sole starter culture, and malted barley as the only substrate. The ingredients and brewing process were carefully monitored to ensure the quality and innocuousness of the beverage. During fermentation, the yeast consumed 89.7% of total sugars and produced 13.8% v/v of ethanol. The product was fermented and then aged for 8 days, adjusted to 5% v/v alcohol, and analyzed. There were no traces of mycotoxins, lead, arsenic, methanol, or microbiological contamination that would compromise consumer health. According to the physicochemical analysis, the final ethanol concentration (5.2% v/v) and other characteristics complied with national and international guidelines. The ethyl acetate and isoamyl alcohol present are known to confer sweet and fruity flavors. The sensory test defined the beverage as refreshing and as having an apple and pear flavor, a banana aroma, and a good level of bitterness. The judges preferred it over a commercial reference sample of Belgian-style pale ale made from S. cerevisiae. Hence, P. kudriavzevii 4A has the potential for use in the beer industry.

Lachancea thermotolerans, an Innovative Alternative for Sour Beer Production

The interest in and growth of craft beer has led to an intense search for new beers and styles. The revival of traditional styles has sometimes been hampered by the use of microorganisms such as lactic acid bacteria. Therefore, studies on alternative yeasts for the production of this style of beer have increased. In this work and together with previous studies carried out with yeasts isolated from Madrid agriculture (from grapes, must, wine, vineyards and wineries), the capacity of 10 yeast strains, belonging to the genus Lachancea thermotolerans, for the production of sour beer has been determined. For this purpose, different fermentation scale-ups (100 mL, 1 L and 100 L) have been performed and their fermentation capacity, aroma compound production (33 volatile compounds by GC), organoleptic profile (trained tasting panel and consumers), melatonin production (HPLC) and antioxidant capacity have been studied. Beer fermented with yeast strain CLI 1232 showed a balanced acidity with a fruity aromatic profile and honey notes. On the other hand, the beer fermented with strain 1-8B also showed a balanced acidity, but less fruity and citric flavour than CLI 1232 strain. Finally, the yeast strain selected by the consumers (CLI 1232) was used for beer production at industrial scale and the market launch of a sour beer.

Commercial craft beers produced in Uruguay: Volatile profile and physicochemical composition

Even beer being the most consumed alcoholic beverage around the world, there is not enough information generated for craft beers produced in Latin America, for either volatile profiles or physicochemical studies. In this work, the chemical and volatile components of ten commercial Blond Ale and nine Indian Pale Ale (IPA) beers from the Uruguayan market were studied using GC-MS. Principal component analysis applied to the data allowed differentiation among the two groups of samples while the volatile compounds and physicochemical parameters responsible for these differences were identified. The physicochemical properties revealed a great diversity between all beer samples even within the same beer style. The main significant differences were obtained for alcohol, polyphenols, bitterness, colour, and pH. Most Blond Ale beer samples were differentiated from IPA ones by raw fermentation aroma compounds such as 1-pentanol, 1-hexanol, hexanoic and isobutyric acids, 4-vinyl guaiacol, and 5,5-dimethyl-2(5H)-furanone. This is the first work that contributes to the knowledge of Uruguayan craft beers. The study also showed the ability of most of the Uruguayan microbreweries to brew Blond Ale and IPA craft beer styles that meet international standards for physicochemical quality.

Bioprospecting of the probiotic potential of yeasts isolated from a wine environment

Autochthonous yeasts of oenological origin are adapted to highly stressful and selective environments, which makes them potential candidates for probiotics. The objective of the present study was to explore the probiotic potential of 96 native yeasts of oenological origin, their biosafety, resistance to gastrointestinal tract conditions and adhesion properties. Regarding biosafety, 66 isolates shown negative hemolytic activity, negative urease activity and susceptibility to 3 or more antifungals. After the gastrointestinal resistance test, 15 isolates were selected that showed growth at different temperatures, tolerance to low pH and the presence of bile salts in in vitro tests. In general, survival after simulated conditions of the gastrointestinal tract was high and more restrictive was the duodenal. The results of the adhesion properties showed highly variable hydrophobicity and a high percentage of autoaggregation at 24 h. The maximum production of biofilm was detected in the Pichia strains. Of a total of 96 yeast strains, 15 non-Saccharomyces yeasts presented suitable properties as probiotic candidates. The native winemaking strains performed better than the reference probiotic strain, Saccharomyces cerevisiae var. boulardii CNCM I-745, which reaffirms that these strains are promising probiotic candidates and further studies are necessary to confirm their probiosis.

Use of Kombucha SCOBY and Commercial Yeast as Inoculum for the Elaboration of Novel Beer

Kombucha is a beverage obtained from fermentation of Camellia sinensis tea using a symbiotic culture of bacteria and yeast (SCOBY). This association of bacteria and yeasts can be an interesting source of microorganisms for developing fermented beverages, including beer. The objective of this study was to evaluate kombucha SCOBY and commercial brewing yeast as a starter culture for the elaboration of beer. Three assays were performed to develop the beverage (C = control, KL = kombucha + yeast, K = kombucha). The pH, density, carbohydrates, organic acids and ethanol were evaluated during fermentation. Microbial counts (yeasts and mesophilic bacteria) and volatile compounds were recorded at the initial and final fermentation times. The content of total phenolic compounds, antioxidant capacity, color and bitterness (IBU) of the beers were determined. The results showed that kombucha-fermented wort produces a beer with differentiated characteristics. Increased lactic acid (0.73 g/L) and low alcohol content (1.3%) were observed in the K assay. Further, desired volatile compounds, such as ethyl octanoate, phenethyl acetate and 2-phenylethanol, were also found in this beer. The combination of kombucha and commercial yeast for beer production showed carbohydrate consumption and contents of organic acids similar to those of control beer, producing beers with an alcohol content of 5.9%. From the results, it was possible to observe a tendency for the content of total phenolic compounds (37.57, 33.00 and 31.64 mg/100 mL for K, KY and C assays, respectively) to increase when the wort was inoculated with kombucha. There was no difference in the antioxidant activity of the produced beers. All produced beers showed a yellowish color and a bitterness value (IBU) of 27%. The present study showed that adding kombucha as a starter culture produced beer with differentiated properties, such as high antioxidant activity, low alcohol content and sour characteristics.

Using wild yeasts to modulate the aroma profile of low-alcoholic meads

In recent years, ample research has focused on applying wild (especially non-Saccharomyces) yeasts in producing alcoholic beverages. Common characteristics of wild yeast strains include simultaneous high production of fruity and floral aroma compounds and low ethanol production. In this study, mead starter cultures were selected based on preliminary screening of wild yeast strains from a Brazilian culture collection (n = 63) for their ability to produce aroma-active compounds. The selected strains included one strain of Saccharomyces cerevisiae and three non-Saccharomyces strains (Pichia jadinii, Torulaspora delbrueckii, and Kluyveromyces lactis). These strains were used to ferment honey must prepared with Aroeira honey, adjusted to 24°Brix, which took 36 days to complete. Single culture fermentations and co-fermentations with S. cerevisiae and non-Saccharomyces strains were carried out. The quality of the produced beverages was evaluated by sugar consumption and production of alcohols and organic acids, analyzed with high-performance liquid chromatography. The volatile organic compound composition was analyzed with gas chromatography-mass spectrometry. Meads with various ethanol amounts (4.7-11.0% v/v) and residual sugar contents (70.81-160.25 g l-1) were produced. In addition, in both single-strain fermentation and co-fermentation with S. cerevisiae, meads produced with either Torulaspora delbrueckii or Kluyveromyces lactis had a roughly three-fold higher content of honey-aroma compound phenethyl acetate and a higher hedonic impression score than meads produced with only S. cerevisiae. These results demonstrated non-Saccharomyces yeasts' ability to increase aroma complexity and improve the sensory quality of low-alcoholic meads.

Non-Conventional Yeast: Behavior under Pure Culture, Sequential and Aeration Conditions in Beer Fermentation

The use of wild yeasts, isolated from different environments, is becoming the most interesting option for the production of new beers. The objective of this study is to evaluate the potential of seven non-conventional yeast strains from five different species (Saccharomyces cerevisiae, Hanseniaspora guilliermondii, Metschnikowia pulcherrima, Torulaspora delbrueckii, and Zygosaccharomyces bailii) isolated from Madrid agriculture to produce type ale beer. Wild yeast strains were evaluated at laboratory and pilot plant scales under different fermentation conditions (pure, aerated, and sequential culture). Strain S. cerevisiae SafAle S-04 was used as a reference. Throughout the fermentation of beer, volatile compounds were determined by GC and residual sugars by HPLC, among other parameters. The yeast strains used for the fermentation in pure culture conditions were unable to ferment maltose and maltotriose (0.73-1.18% v/v of ethanol). The results of the study under aerated conditions showed varying levels of higher alcohol and ester concentrations. It should be noted that the strain CLI 1057 (S. cerevisiae) fermented maltose in the presence of oxygen (Kluyver effect). This strain also showed a high production of 4-vinyl guaiacol, making it suitable for producing beers with a phenolic profile. Finally, three strains (H. guilliermondii, Z. bailii, and T. delbrueckii) were evaluated in sequential culture together with commercial strain and found to improve the organoleptic characteristics of the brewed beer. These approaches offer the opportunity to add new product characteristics to the beers.

Increased volatile thiol release during beer fermentation using constructed interspecies yeast hybrids

Interspecies hybridization has been shown to be a powerful tool for developing and improving brewing yeast in a number of industry-relevant respects. Thanks to the popularity of heavily hopped ‘India Pale Ale’-style beers, there is an increased demand from brewers for strains that can boost hop aroma. Here, we explored whether hybridization could be used to construct strains with an enhanced ability to release hop-derived flavours through β-lyase activity, which releases desirable volatile thiols. Wild Saccharomyces strains were shown to possess high β-lyase activity compared to brewing strains, however, they also produced phenolic off-flavours (POF) and showed poor attenuation. To overcome these limitations, interspecies hybrids were constructed by crossing pairs of one of three brewing and one of three wild Saccharomyces strains (S. uvarum and S. eubayanus). Hybrids were screened for fermentation ability and β-lyase activity, and selected hybrids showed improved fermentation and formation of both volatile thiols (4MMP, 3MH and 3MH-acetate) and aroma-active esters compared to the parent strains. Undesirable traits (e.g. POF) could be removed from the hybrid by sporulation. To conclude, it was possible to boost the release of desirable hop-derived thiols in brewing yeast by hybridization with wild yeast. This allows production of beer with boosted hop aroma with less hops (thus improving sustainability issues).

Influence of Different Aggregation States on Volatile Organic Compounds Released by Dairy Kluyveromyces marxianus Strains

Kluyveromyces marxianus has the ability to contribute to the aroma profile of foods and beverages since it is able to produce several volatile organic compounds (VOCs). In this study, 8 dairy K. marxianus strains, previously selected for their adhesion properties, were tested for VOCs production when grown in different conditions: planktonic, biofilm-detached, and MATS forming-cells. It was shown that biofilm-detached cells were mainly able to produce higher alcohols (64.57 mg/L), while esters were mainly produced by planktonic and MATS forming-cells (117.86 and 94.90 mg/L, respectively). Moreover, K. marxianus biofilm-detached cells were able to produce VOCs with flavor and odor impacts, such as ketons, phenols, and terpenes, which were not produced by planktonic cells. In addition, specific unique compounds were associated to the different conditions tested. Biofilm-detached cells were characterized by the production of 9 unique compounds, while planktonic and MATS forming-cells by 7 and 12, respectively. The obtained results should be exploited to modulate the volatilome of foods and beverages and improve the production of certain compounds at the industrial level. Further studies will be carried out to better understand the genetic mechanisms underlying the metabolic pathways activated under different conditions.

Lentil Fortification and Non-Conventional Yeasts as Strategy to Enhance Functionality and Aroma Profile of Craft Beer

During the last few years, consumer demand has been increasingly oriented to fermented foods with functional properties. This work proposed to use selected non-conventional yeasts (NCY) Lachanceathermotolerans and Kazachstaniaunispora in pure and mixed fermentation to produce craft beer fortified with hydrolyzed red lentils (HRL). For this, fermentation trials using pils wort (PW) and pils wort added with HRL (PWL) were carried out. HRL in pils wort improved the fermentation kinetics both in mixed and pure fermentations without negatively affecting the main analytical characters. The addition of HRL determined a generalized increase in amino acids concentration in PW. L. thermotolerans and K. unispora affected the amino acid profile of beers (with and without adding HRL). The analysis of by-products and volatile compounds in PW trials revealed a significant increase of some higher alcohols with L. thermotolerans and ethyl butyrate with K. unispora. In PWL, the two NCY showed a different behavior: an increment of ethyl acetate (K. unispora) and β-phenyl ethanol (L. thermotolerans). Sensory analysis showed that the presence of HRL characterized all beers, increasing the perception of the fruity aroma in both pure and mixed fermentation.

Beer Safety: New Challenges and Future Trends within Craft and Large-Scale Production

The presence of physical, chemical, or microbiological contaminants in beer represents a broad and worthy problem with potential implications for human health. The expansion of beer types makes it more and more appreciated for the sensorial properties and health benefits of fermentation and functional ingredients, leading to significant consumed quantities. Contaminant sources are the raw materials, risks that may occur in the production processes (poor sanitation, incorrect pasteurisation), the factory environment (air pollution), or inadequate (ethanol) consumption. We evaluated the presence of these contaminants in different beer types. This review covers publications that discuss the presence of bacteria (Lactobacillus, Pediococcus), yeasts (Saccharomyces, Candida), moulds (Fusarium, Aspergillus), mycotoxins, heavy metals, biogenic amines, and micro- and nano-plastic in beer products, ending with a discussion regarding the identified gaps in current risk reduction or elimination strategies.

Fruit Microbial Communities of the Bisucciu Sardinian Apricot Cultivar (Prunus armeniaca L.) as a Reservoir of New Brewing Starter Strains

Local fruit cultivars may improve the originality of specialty beers both directly, by conferring peculiar tastes and flavors, and indirectly, as a reservoir of new starter strains. Accordingly, the fungal and bacterial communities of Bisucciu fruit, a Sardinian apricot cultivar used to produce a local fruit beer, were here investigated by culture-dependent methods. From the 16S rDNA and ITS sequence analyses of 68 epiphytic isolates, 5 bacterial species and 19 fungal species were identified. Aureobasidium pullulans and Rhodotorula glutinis were the dominant fungal species, while Enterococcus mundtii (Firmicutes) and Frigoribacterium faeni (Actinobacteria) were the most represented species among bacterial isolates. Enrichment cultures of fresh apricot puree, followed by fermentation trials in beer wort and beer wort added with apricot puree, allowed the selection of four isolates of Pichia kudriavzevii, Hanseniaspora uvarum, H. pseudoguilliermondii, and H. clermontiae able to dominate over the Bisucciu native microbiota and to produce from 0.57% to 0.74% (vol/vol) of ethanol. HS-SPME-GC/MS analysis highlighted a significant increase in the ester and alcohol fractions as well as a reduction in terpenes after fermentation with the selected yeasts. Results obtained suggest that the yeast isolates may contribute to the definition of the taste and flavor of beers when used in mixed fermentations with Saccharomyces.

The cell wall and the response and tolerance to stresses of biotechnological relevance in yeasts

In industrial settings and processes, yeasts may face multiple adverse environmental conditions. These include exposure to non-optimal temperatures or pH, osmotic stress, and deleterious concentrations of diverse inhibitory compounds. These toxic chemicals may result from the desired accumulation of added-value bio-products, yeast metabolism, or be present or derive from the pre-treatment of feedstocks, as in lignocellulosic biomass hydrolysates. Adaptation and tolerance to industrially relevant stress factors involve highly complex and coordinated molecular mechanisms occurring in the yeast cell with repercussions on the performance and economy of bioprocesses, or on the microbiological stability and conservation of foods, beverages, and other goods. To sense, survive, and adapt to different stresses, yeasts rely on a network of signaling pathways to modulate the global transcriptional response and elicit coordinated changes in the cell. These pathways cooperate and tightly regulate the composition, organization and biophysical properties of the cell wall. The intricacy of the underlying regulatory networks reflects the major role of the cell wall as the first line of defense against a wide range of environmental stresses. However, the involvement of cell wall in the adaptation and tolerance of yeasts to multiple stresses of biotechnological relevance has not received the deserved attention. This article provides an overview of the molecular mechanisms involved in fine-tuning cell wall physicochemical properties during the stress response of Saccharomyces cerevisiae and their implication in stress tolerance. The available information for non-conventional yeast species is also included. These non-Saccharomyces species have recently been on the focus of very active research to better explore or control their biotechnological potential envisaging the transition to a sustainable circular bioeconomy.

Metabolomics of Non-Saccharomyces Yeasts in Fermented Beverages

Fermented beverages have been consumed for millennia and today support a global industry producing diverse products. Saccharomyces yeasts currently dominate the fermented beverage industry, but consumer demands for alternative products with a variety of sensory profiles and actual or perceived health benefits are driving the diversification and use of non-Saccharomyces yeasts. The diversity of flavours, aromas, and other sensory characteristics that can be obtained by using non-Saccharomyces yeasts in fermentation is, in large part, due to the diverse secondary metabolites they produce compared to conventional Saccharomyces yeast. Here, we review the use of metabolomic analyses of non-Saccharomyces yeasts to explore their impact on the sensory characteristics of fermented beverages. We highlight several key species currently used in the industry, including Brettanomyces, Torulaspora, Lachancea, and Saccharomycodes, and emphasize the future potential for the use of non-Saccharomyces yeasts in the production of diverse fermented beverages.

Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation

Abstract

There is a growing appreciation for the role that yeast play in biotransformation of flavour compounds during beverage fermentations. This is particularly the case for brewing due to the continued popularity of aromatic beers produced via the dry-hopping process. Here, we review the current literature pertaining to biotransformation reactions mediated by fermentative yeasts. These reactions are diverse and include the liberation of thiols from cysteine or glutathione-bound adducts, as well as the release of glycosidically bound terpene alcohols. These changes serve generally to increase the fruit and floral aromas in beverages. This is particularly the case for the thiol compounds released via yeast β-lyase activity due to their low flavour thresholds. The role of yeast β-glucosidases in increasing terpene alcohols is less clear, at least with respect to fermentation of brewer’s wort. Yeast acetyl transferase and acetate esterase also have an impact on the quality and perceptibility of flavour compounds. Isomerization and reduction reactions, e.g. the conversion of geraniol (rose) to β-citronellol (citrus), also have potential to alter significantly flavour profiles. A greater understanding of biotransformation reactions is expected to not only facilitate greater control of beverage flavour profiles, but also to allow for more efficient exploitation of raw materials and thereby greater process sustainability.

Key points

• Yeast can alter and boost grape- and hop-derived flavour compounds in wine and beer

• β-lyase activity can release fruit-flavoured thiols with low flavour thresholds

• Floral and citrus-flavoured terpene alcohols can be released or interconverted

Impact of Non-Saccharomyces Wine Yeast Strains on Improving Healthy Characteristics and the Sensory Profile of Beer in Sequential Fermentation

The use of non-Saccharomyces yeasts in brewing is a useful tool for developing new products to meet the growing consumer demand for innovative products. Non-Saccharomyces yeasts can be used both in single and in mixed fermentations with Saccharomyces cerevisiae, as they are able to improve the sensory profile of beers, and they can be used to obtain functional beers (with a low ethanol content and melatonin production). The aim of this study was to evaluate this capacity in eight non-Saccharomyces strains isolated from Madrid agriculture. For this purpose, single fermentations were carried out with non-Saccharomyces strains and sequential fermentations with non-Saccharomyces and the commercial strain SafAle S-04. The Wickerhamomyces anomalus strain CLI 1028 was selected in pure culture for brewing beer with a low ethanol content (1.25% (v/v)) for its fruity and phenolic flavours and the absence of wort flavours. The best-evaluated strains in sequential fermentation were CLI 3 (Hanseniaspora vineae) and CLI 457 (Metschnikowia pulcherrima), due to their fruity notes as well as their superior bitterness, body, and balance. Volatile compounds and melatonin production were analysed by GC and HPLC, respectively. The beers were sensory-analysed by a trained panel. The results of the study show the potential of non-Saccharomyces strains in the production of low-alcohol beers, and as a flavour enhancement in sequential fermentation.

Identification of non-Saccharomyces yeast strains isolated from local traditional sorghum beer produced in Abidjan district (Côte d'Ivoire) and their ability to carry out alcoholic fermentation

Studies on yeasts involved in traditional sorghum beer fermentation in several African countries revealed the presence of two groups: Saccharomyces and non-Saccharomyces. If Saccharomyces strains were reputed for their fermentation performances, the non-Saccharomyces yeast strains have been recognized for their contribution towards the improvement of the beverage's organoleptic quality, justifying their use as aromatic starter. In spite of this contribution, most studies were focused only on Saccharomyces strains as starter. In this work, the non-Saccharomyces yeast strains found in the inoculum of traditional sorghum beer was investigated. Identification of non-Saccharomyces yeast strains by PCR-RLFP followed sequencing of D1/D2 domain revealed the presence of 2 species: Issatckenkia orientalis and Pichia kudriavzevii with Issatckenkia orientalis predominating. Out of the two species, fermentation characteristics showed that Issatckenkia orientalis seemed suitable for sorghum beer production.

New Approaches for the Fermentation of Beer: Non-Saccharomyces Yeasts from Wine

Non-Saccharomyces yeasts represent a very attractive alternative for the production of beers with superior sensory quality since they are able to enhance the flavour of beer. Furthermore, they can produce beers with low ethanol content due to the weak fermentative capacity of a large percentage of non-Saccharomyces species. The objective of this study was to evaluate the ability of 34 non-Saccharomyces yeast strains isolated from Madrilenian agriculture to produce a novel ale beer. The non-Saccharomyces yeast strains were screened at two scales in the laboratory. In the first screening, those with undesirable aromas were discarded and the selected strains were analysed. Thirty-three volatile compounds were analysed by GC, as well as melatonin production by HPLC, for the selected strains. Thirteen strains were then fermented at a higher scale in the laboratory for sensory evaluation. Only yeast strains of the species Schizosaccharomyces pombe and Lachancea thermotolerans were able to complete fermentation. Species such as Torulaspora delbrueckii, Metschnikowia pulcherrima, Wickerhamomyces anomalus, Hanseniaspora vineae, and Hanseniaspora guilliermondii could be used both for production of low ethanol beers and co-fermentation with a Saccharomyces yeast to improve the organoleptic characteristics of the beer. In addition, for these strains, the levels of melatonin obtained were higher than the concentrations found for Saccharomyces strains subjected to the same study conditions. The selected strains can be used in future trials to further determine their viability under different conditions and for different purposes.

The synthesis of soluble and volatile bioactive compounds by selected brewer's yeasts: Antagonistic effect against enteropathogenic bacteria and food spoiler - toxigenic Aspergillus sp

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Brewing fermentation residue possesses bacteriostatic and fungicidal activity.

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Crude brewing fermentation residue is an antimicrobial agent.

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Brewer’s yeasts secrete soluble and volatile bioactive compounds.

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Ethanol and 2,3-butanediol possess bacteriostatic and antifungal properties.

Contamination by Aspergillus sp. and the accumulation of its mycotoxins in food and beverages have a high impact on human health and food safety. This investigation inquires the ability of brewer’s yeasts discarded after fermentation (brewing fermentation residue, BFR) to synthesize bioactive compounds and to biocontrol Aspergillus sp. BFRs of Saccharomyces cerevisiae MBELGA62 and Pichia kudriavzevii MBELGA61 proved to have bacteriostatic properties and to be efficient in fungal growth reduction, decreasing the growth rate of Aspergillus flavus and Aspergillus parasiticus up to 37.8% and 42.5%, respectively. Fungal mycelium degradation along with absentia of conidia was detected near the yeast inoculum. Moreover, the yeasts synthesize volatile bioactive compounds that extend Aspergillus sp. lag phase above 100% and decrease fungal growth rates from 20% towards 44%, along with the complete inhibition of conidia synthesis. These results indicate the potential of this residue to be used in biocontrol applications in the food industry.

Functional Characterization of khadi Yeasts Isolates for Selection of Starter Cultures

Yeasts play an important role in spontaneous fermentation of traditional alcoholic beverages. Our previous study revealed that a mixed-consortia of both Saccharomyces and non-Saccharomyces yeasts were responsible for fermentation of khadi, a popular, non-standardized traditional beverage with an immense potential for commercialization in Botswana. Functional characterization of isolated fermenting yeasts from mixed consortia is an indispensable step towards the selection of potential starter cultures for commercialization of khadi. In this study, we report the characterization of 13 khadi isolates for the presence of brewing-relevant phenotypes such as their fermentative capacity, ability to utilize a range of carbon sources and their ability to withstand brewing-associated stresses, as a principal step towards selection of starter cultures. Khadi isolates such as Saccharomyces cerevisiae, Saccharomycodes ludwigii and Candida ethanolica showed good brewing credentials but Lachancea fermentati emerged as the isolate with the best brewing attributes with a potential as a starter culture. However, we were then prompted to investigate the potential of L. fermentati to influence the fruity aromatic flavor, characteristic of khadi. The aroma components of 18 khadi samples were extracted using headspace solid phase micro-extraction (HSSPME) and identified using a GC-MS. We detected esters as the majority of volatile compounds in khadi, typical of the aromatic signature of both khadi and L. fermentati associated fermentations. This work shows that L. fermentati has potential for commercial production of khadi.

Brettanomyces bruxellensis: Overview of the genetic and phenotypic diversity of an anthropized yeast

Human-associated microorganisms are ideal models to study the impact of environmental changes on species evolution and adaptation because of their small genome, short generation time, and their colonization of contrasting and ever-changing ecological niches. The yeast Brettanomyces bruxellensis is a good example of organism facing anthropogenic-driven selective pressures. It is associated with fermentation processes in which it can be considered either as a spoiler (e.g. winemaking, bioethanol production) or as a beneficial microorganism (e.g. production of specific beers, kombucha). Besides its industrial interests, noteworthy parallels and dichotomies with Saccharomyces cerevisiae propelled B. bruxellensis as a valuable complementary yeast model. In this review, we emphasize that the broad genetic and phenotypic diversity of this species is only beginning to be uncovered. Population genomic studies have revealed the co-existence of auto- and allotriploidization events with different evolutionary outcomes. The different diploid, autotriploid and allotriploid subpopulations are associated with specific fermented processes, suggesting independent adaptation events to anthropized environments. Phenotypically, B. bruxellensis is renowned for its ability to metabolize a wide variety of carbon and nitrogen sources, which may explain its ability to colonize already fermented environments showing low-nutrient contents. Several traits of interest could be related to adaptation to human activities (e.g. nitrate metabolization in bioethanol production, resistance to sulphite treatments in winemaking). However, phenotypic traits are insufficiently studied in view of the great genomic diversity of the species. Future work will have to take into account strains of varied substrates, geographical origins as well as displaying different ploidy levels to improve our understanding of an anthropized yeast's phenotypic landscape.